In order to promote adhesion between rubber and ferrous metals it is known to employ a variety of metallic salts as coatings to the metal or as an ingredient in a rubber composition. It is also known to add various resins as tackifiers and/or adhesion promoters and, in other instances, to employ both a metal salt and a resin. In still other instances it is known to add halogenated rubber to the rubber stock along with an organic complex of cobalt or nickel. Inasmuch as the present invention does not employ metallic salts, resins or organic complexes of cobalt or nickel, patents disclosed thereto are not relevant to the subject application apart from the fact that the components they teach improve the adhesion between rubber and metal.
With respect to the addition of halogenated rubber or polymers to vulcanizable rubber stocks, or the use of halogenated rubbers as adhesives, the general teaching in the art includes the following patents.
U.S. Pat. No. 2,482,600 discloses a heat resistant vulcanizable rubber and method for imparting heat resistance which is based upon the addition of unvulcanized polychloroprene with a copolymer of butadiene and acrylonitrile. Rubber-to-metal adhesion is neither taught nor suggested.
U.S. Pat. No. 2,581,920, owned by the Assignee of record herein, discloses an adhesive composition including a solvent, a dichlorobutadiene resin and chlorinated rubber for adhering natural as well as various synthetic rubbers to metallic substrates. The adhesive functions as a cement between the two materials and is not added to the natural or synthetic rubber but is rather used to coat one or both of the layers.
U.S. Pat. No. 3,596,753 discloses a rubber mixture comprising polychloroprene and nitrile rubber which is reinforced with metallic wire such as zinc-coated steel. The patent teaches that the rubber composition is heat resistant and is, therefore, useful for heat resistant conveyor belts. In order to promote rubber-to-metal adhesion, inorganic cobalt complexes are disclosed.
U.S. Pat. No. 3,645,934 discloses a process whereby natural rubber, polychloroprene and an EPDM rubber are compounded with carbon black to prepare vulcanizable, ozone resistant compositions. Again, while halogenated rubbers are combined with natural rubber, improved metal adhesion is not suggested.
Lastly, two recent U.S. patents of ours, owned by the Assignee of record herein, Nos. 4,267,079 and 4,376,838 actually disclose the use of certain halogenated rubbers, e.g., neoprene and chlorobutyl, with natural rubber in conjunction with an organic complex of cobalt or nickel or salt of cobalt or nickel with an aliphatic fatty acid in order to improve adhesion between the rubber and metallic reinforcement embedded therein.
We have also found that improved rubber-to-metal adhesion is obtained by the use of the halogenated rubber alone without any cobalt, nickel or other transition metal complexes or salts that are usually added for the sole purpose of improving rubber-to-metal adhesion, thereby effecting a savings by the elimination of these compounds which are generally costly.